Grafted verticordia cultivation

Introduction

To ensure longevity and productivity of Verticordia as cutflowers or amenity plants, grafting onto suitable rootstocks may be necessary.

The genus Verticordia is part of the Myrtaceae family, and closely related to waxflowers (Chamelaucium species). Several waxflowers are suitable rootstocks for grafting Verticordia scions. By careful selection of rootstocks, grafting can assist plants to survive in various soils.

Selections

Two Verticordia selections have been successfully grafted onto waxflower rootstocks: the bright red large-flowered semi-terminal V. etheliana and the yellow small-flowered V. chrysostachys.

Plants of V. etheliana flowered at Medina, south of Perth from July to November with some flowers into December. V. chrysostachys flowered from November to January with a peak in December.

Both grafted species survived well in cultivation, produced moderate stem numbers with a range of short to moderate stem lengths and a vase life exceeding two weeks. Their form lends well to a low to medium height border amenity plant requiring minimal maintenance.

Suitable soils

Grafted verticordias prefer sand over gravel at 1m although they can be grown in deep sand provided the water supply is maintained. Soil pH in the range 5.5 to 6.5 (in water) is preferred.

The site should be free from dieback (Phytophthora) and nematodes, and prepared ahead of planting, eliminating all weeds. Compacted sites should be deep-ripped to produce a suitable seedbed.

Allow sufficient time for the ground to settle before planting. Great care must be taken to apply good hygiene practices to prevent introduction of disease.

Planting and establishment

Use disease-free plants. The best time to plant is late autumn or early spring in warmer areas or late spring in cooler areas.

Ensure plants are not root-bound. If so, the root system will need to be teased out during planting. The seedbed must be thoroughly wetted up at least a week before planting.

Grafts can be brittle and therefore care needs to be taken when handling and planting. Individual wind breaks or tree guards for the first three months after planting may be necessary on windy sites.

Grafted verticordias perform best in dense plantings to maximise yield per square metre of land and to encourage upward stem growth. This can be achieved by preparing a bed 1.2m wide and planting in double rows with 0.6m between rows and 1.0m between plants in the row and planting in a staggered pattern (see below). 

These can be arranged in 50 to 100m rows with workways between rows centred at 3m. Depending on the spacing this gives a plant density of 3300 to 6600 plants per hectare. Best light interception is usually achieved if rows are aligned north-south.

It is also beneficial to use mulch to reduce weed competition, moderate soil temperature and conserve moisture. In cooler regions plastic mulch or ‘weed mat’ has been found suitable, while in hotter climates white plastic mulch or straw works better.

Irrigation

Grafted verticordias should be planted into moist soil and watered regularly during establishment using drippers, particularly on sandy soils.

In summer, watering may need to be split into two to three applications per day depending on evaporation replacement required. This usually requires an automatic watering system. Once established, grafted verticordias are low water users (50% evaporation replacement or 4 litres per day per plant in summer in the Perth region).

Fertilisers

At planting, 10g of low phosphorus slow release fertiliser such as ‘for native plants' should be spread on the soil surface (not in the planting hole) adjacent to the plants.

Once established, plants (at two to three months) require a regular feed, preferably through the irrigation lines such that plants receive 150kg/ha of nitrogen, 115kg/ha potassium and 7kg/ha of phosphorus and calcium together with a balance of trace elements each year.

Injecting fertilisers during watering (fertigation) is an efficient way to meet the nutrition requirements of plants.  This can be achieved by making up a stock solution of fertilisers in a 200 litre drum of water for pressure injection (see Table 1 for stock solution rates).

In summer fertigate plants daily. The concentration of fertilisers injected (particularly nitrogen) should be scaled back during autumn.

In winter fertigate every third day then increase frequency through spring. During each watering allow the irrigation system to run for 10 minutes without fertiliser. Then inject 10 litres of the stock solution per 800 plants being watered over the next 40 minutes, followed by 5 to 10 minutes of watering without fertiliser.

Acclimatise young plants to the fertiliser program by starting at the low rate (Table 1) and gradually increasing the frequency of injection over the first year and then increasing the rate in the second year until irrigated daily.

Pruning

Plants should be lightly pruned in the first year to encourage branching. Thereafter they should be pruned to about one-third of their height, as this will encourage long stem production. It may be necessary to allow plants to grow for two years to produce sufficient stem length.

Pests and diseases

Plants are susceptible to botrytis and mildew, particularly in moist weather during early autumn, which can cause leaf drop.  They are also attacked by a range of insects including thrips, nitatulid beetles, weevils, caterpillars and scale.

Plants may need regular spraying with a registered fungicide to control diseases.  Monitoring and field control of insects is essential coupled with an effective postharvest treatment, such as insecticide and fungicide dips, to provide sufficient level of kill to meet overseas quarantine inspections.

Postharvest management

Flowers can be a handled as for waxflower. Flowers should be cooled at 1°C to 5°C as soon as possible after harvest and will benefit from forced-air cooling after picking to remove field heat. Lengthy delays in removing field heat can seriously affect flower quality.

Flowers have a low ethylene flower drop response, although pulsing with silver thiosulphate may lengthen vase life. Alternatively, placing 1-MCP sachets (EthylBloc®) in flower boxes may be effective at controlling ethylene response.

Further reading

https://rirdc.infoservices.com.au/items/12-110

Acknowledgements

The support, cooperation and assistance of the Australian wildflower industry is gratefully appreciated.

Funding support from the Rural Industries Research and Development Corporation and the Department of Agriculture and Food is acknowledged.